An important and integral part of the peripheral equipment supporting present-day digital computer systems is the magnetic memory equipment commonly used to store data at terminal facilities. One familiar form of such equipment is a disk file comprising a number of rotating disk surfaces, with concentric tracks on which signals are magnetically recorded and associated magnetic transducers arranged to confront one (or several) of these surfaces for writing and reading.
Workers in the disk file art will recognize that where early disk files operated according to a "core-per-track" mode or a "core-per-surface" mode, an intermediate mode, more recently suggested, involves a "core-per-zone" mode -- whereby each core "covers" a prescribed number of adjacent disk tracks and is translated across these relatively quickly and efficiently. Typically, a multi-core head, involving about one dozen heads, may be assembled and mounted as a low-mass load apt to be quickly and very accurately reciprocated across this excursion distance -- typically the order of 20 to 30 mils, with each core typically swept across about 30 to 50 adjacent tracks.
This presents a miniaturized, multi-core head which may be independently mounted and separately actuated; being characterized as a "core-per-zone" arrangement, better understood by reference to U.S. Pat. No. 3,686,649 to Behr and U.S. Pat. No. 4,007,493 to Behr et al.; these being hereby incorporated herein by reference.
Now, such transducer heads which are to be translated over relatively short distances -- on the order of 20 or 30 mils -- usually place a premium on access-speed and accuracy. According to one feature of this invention, it has been found useful to mount such heads on flexure pivots and actuate them directly, with electro-magnet motive means, like a voice-coil, which are field-coupled only, not mechanically coupled. Voice-coils and flexure pivots are made for such short excursion distances; also, they can accommodate the very fast acceleration (low mass) necessary for fast accessing speeds and can operate at the relatively low power, with low-mass, that is optimum for such disk file equipment.
As workers in the art well know, such transducers (recording heads) must be brought very closely adjacent the rapidly-rotating disk surface for effective transducing operations. Thus, head/disk clearance is very, very small, as are the separations between recording tracks. And, as workers recognize, the mounting/positioning arrangement for such heads must be extremely stable, as well as being positionable very fast yet with great accuracy and reliability. That is, it is obviously critical that a head be mounted and translated very quickly and precisely as it is shifted radially from track-to-track across a disk. Otherwise, writing and reading cannot be performed reliably enough and/ or fast enough. THis invention is intended to improve upon known head positioning arrangements, and especially access speed.
Now, workers recognize that the recording track density of present day magnetic recording disks must be increased; for instance, the recording tracks should be spaced closer together where possible. Of course, this makes head positioning ever more difficult. Typically, a recording head unit will present a plurality of individual magnetic transducers, each for recording on an individual magnetic recording track. Because of the tight positioning tolerances, the recording tracks are typically "interlaced" between recording heads to save space. But, with such interlacing, the heads must be positioned and centered very precisely to avoid "cross-talk" between adjacent tracks.
Workers will recall various arrangements commonly known in the art for track positioning of magnetic heads -- e.g., with mechanical arms driven by electrical actuators or by levers and cams, etc., or by pneumatically-actuated diaphragms, or with related hydraulic means, and so forth. These and related features are described and/or referenced in U.S. Pat. Nos. 3,864,749, 3,696,351 and 3,320,599.
Systems according to the present invention contemplate such arrangements whereby a multi-head mount is adapted to be translated with great precision and speed across the surface of a magnetic disk, these involving improvements adapted to enhance the storage capacity and decrease the data access time in disk file equipment but at relatively low cost per byte.
In one particular embodiment, a head mount is supported by flexure-spring means for pivotal translation by an electromagnetic actuator system (e.g., a voice-coil actuator, or a pair of them). Such systems will be seen as highly effective; allowing fast, precise translation over short excursions, yet doing so in a low-mass, low-power system -- one permitting the heads to be actuated independently, while eliminating the friction associated with prior art mechanisms. Positioners according to the invention will be recognized as very convenient and versatile to use, the actuator components being commonly available, as well as disposed to be readily accessible and replaceable. It will accommodate tandem positioners, such as a "dual, in-line" actuator arrangement disclosed below. Such systems will also be seen as apt for use in conjunction with a "track-on-data" servo arrangement.
By comparison, conventional positioners are more complex and less efficient -- typically involving a head mount suspended, by a spring system, on a rigid base member which is moveably disposed in slide-ways or the like -- and, usually, supported by bearings as well. The performance of such positioning systems leaves something to be desired in several respects. For instance, conventional "linear" positioning actuators, having an excursion on the order of several inches, are relatively slow -- having an (average) actuation time on the order of 25-50 MS and requiring hundreds of watts of power -- in some cases exceeding a kilowatt. With earlier disk files, actuation power was obtained hydraulically, further limiting response time and operating characteristics.